help me in DAC using 89c4051

It is pretty sure that the OP is confused about the message posted.

The pins P1.0 and P1.1 of AT80C4051 are the Analog comparator inputs,
this microcontroller does not have an internal ADC or DAC peripheral.

The R/C method described in the Atmel appnote gives an example of how
to use about 5pins (including P1.0 and P1.1) to create a 5-8bits of ADC.

For the DAC implementation the SAR example from Intel describes how to
build an R/2R ladder to create the DAC section (half of the SAR system).

Another option is to use an external DAC or ADC set up with bit-banged I2C
on P1.0 and P1.1 (SDA/SCL)

Too many options with microcontrollers, even for this aged one.

It is pretty sure that the OP is confused about the message posted.

The pins P1.0 and P1.1 of AT80C4051 are the Analog comparator inputs,
this microcontroller does not have an internal ADC or DAC peripheral.

The R/C method described in the Atmel appnote gives an example of how
to use about 5pins (including P1.0 and P1.1) to create a 5-8bits of ADC.

For the DAC implementation the SAR example from Intel describes how to
build an R/2R ladder to create the DAC section (half of the SAR system).

Another option is to use an external DAC or ADC set up with bit-banged I2C
on P1.0 and P1.1 (SDA/SCL)

Too many options with microcontrollers, even for this aged one.

I am using 89c4051 to convert digital to analog. pin 1.0 and 1.1 are used, but I am confused how to us? please help me I don't know anything.
since you "don't know anything" why not choose a derivative with a DAC, there are many, instead of "this aged one".

Erik

Ya you are right but. But my company has suggested me to use this one.

So this is part of your job?